Inside a Pressure-Assisted Toilet

Pressure-Assisted vs. Gravity-Flow Toilets

Steve Hallo

From the outside, toilets can take on many appearances--they can use an elongated bowl, for example, or use a sleek one-piece design. Inside, though, the working guts of the toilet will use one of only two designs. Either the toilet will use a traditional gravity-flow operation, or it will use a pressure-assisted mechanism.

Pressure-assisted models are usually found in commercial settings, like restaurants, although they are starting to become more common in residential bathrooms. Power-assisted toilets are based on a tank-inside-tank model. As water pumps into the toilet tank from the water supply valve, it creates air-pressure in the tank chamber. This sets the stage for a slightly different type of flush cycle that what occurs in a gravity flow toilet.

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How a Pressure-Assisted Toilet Works

When a pressure-assisted toilet is flushed, the compressed air in the air chamber is released. With the pressure joining the force of gravity, the downward flush is somewhat explosive, leading to a very quick and efficient emptying of the toilet bowl.

You might think this would make pressure assisted toilets very popular. But the drawback is that the explosive flush can be quite loud, which is enough to dissuade many people from wanting such a toilet in the home. Another drawback for many homeowners is that the mechanism seems unusual and may be hard to purchase.

In reality, however, a pressure-assisted toilet mechanism is relatively simple, consisting only of a sealed plastic drum, a flush cartridge, and a water intake valve. While all manufacturers of pressure-assisted toilets use identical parts, most hardware stores don’t carry them. And although plumbing supply houses carry the repair parts, they very rarely sell to non-plumbers.

Pros and Cons of a Pressure-Assisted Toilet

Advantages

Disadvantages

Noisy flush

Difficulty in procuring replacement parts.

More expensive than gravity-flow models.

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A New Innovation

A recent innovation in toilet plumbing is the vacuum-assist toilet. Like a pressure-assist toilet, the vacuum-assist toilet has an inner water tank. But inside the inner tank is a vacuum tank that connects directly to the toilet trap. When the flush occurs, water flowing out of the tank creates a suction force that pulls waste out of the bowl. While both gravity-flow and pressure-assist toilets essentially push waste out of the toilet both, the vacuum assist toilet pulls it out.

Advantages

Easy to repair. Because vacuum-assist toilets use the same water supply and flush valves as gravity models, they're simple to repair.

Strong flush. Vacuum-assist toilets outperform most gravity types but aren't as effective as some pressure-assist toilets.

Like pressure-assist models, vacuum-assist toilets store water in an inner tank, which means moisture doesn't condense on the porcelain tank.